Everybody wants beautiful, healthy hair and skin. For most people, grooming and maintenance of hair and skin is a daily process. The demand for products that improve the look and feel of these surfaces has created a huge industry. Beauty care technology has advanced the cleaning, protection, and restoration of desirable.
Hair properties by altering the hair surface. For many years, especially in the second half of the twentieth century, scientists have focused on the physical and chemical properties of hair to consistently develop products which alter the health, feel,shine, color, softness, and overall aesthetics of hair. Hair care products such as shampoos and conditioners aid the maintenance and grooming process. Shampoos clean the hair and skin oils, and conditioners repair hair damage and make the
hair easier to comb; prevent flyaway; and add feel, shine, and softness. Mechanical processes such as combing, cutting, and blowdrying serve to style the hair.
Chemical products and processes such as chemical dyes, colorants, bleaches, and permanent wave treatments enhance the appearance and hue of the hair. Of particular interest is how all these common hair care items deposit onto hair and change its properties, since these properties are closely tied to product performance. The fact that companies like Procter & Gamble, L’Oreal, and Unilever have hair care product sales consistently measured in billions of US dollars suggests that understanding the science behind human hair has more than just purely academic benefits, as well.
While products and processes such as combing, chemical dyeing, and permanent wave treatment are used to enhance appearance and style of the hair, they also contribute a large amount of chemical and mechanical damage to the fibers, which leads to the degradation of structure and mechanical properties.Asaresult,thefibers become weak and more susceptible to breakage after time, which is undesirable for healthy hair. Shampoos and conditioners which typically serve cleaning and repairing functions to the hair surface, respectively, have a distinct effect on mechanical properties as well.
The tribology of the hair also changes as a function of the various hair care products and processes. Figure 1.8 illustrates schematically various functions, along with the macro- and micro/nanoscale mechanisms behind these interactions that make surface roughness, friction, and adhesion very important to hair and skin.
Desired features and corresponding tribological attributes of conditioners are listed in Table 1.4 For a smooth, wet and dry feel, friction between hair and skin should be minimized in wet and dry envi-ronments, respectively. For a good feel with respect to bouncing and shaking of the hair during walking or running, friction between hair fibers and groups of hair fibers should be low. The friction one feels during combing is a result of interactions between hair and the comb material (generally a plastic), and this too needs to be low to easily maintain, sculpt, and comb the hair. To minimize entanglement, adhesive force (the force required to separate the hair fibers) needs to be low. In
other cases, a certain level of adhesion may be acceptable and is often a function of the hair style. For individuals seeking “hair alignment,” where hair fibers lay flat and parallel to each other, a small amount of adhesive force between fibers may be desired. For more complex and curly styles, even higher adhesion between fibers may be optimal.